Oxygen Vacancy-Rich\nAmorphous ZnCr Oxides Combined\nwith Zeolites for Highly Active and Stable Conversion of Syngas into\nLight Olefins

The remarkable selectivity of light olefins makes bifunctional\ncatalysis a highly promising technique for directly producing light\nolefins from syngas. Amorphous ZnCr oxides were synthesized by low-temperature\ncalcination in a H<sub>2</sub> atmosphere and combined with SAPO-34\nzeolites to convert syngas to light olefins. The characterizations\nrevealed that the amorphous ZnCr oxides exhibited a noteworthy capability\nto adsorb and activate more CO molecules due to a larger specific\nsurface area and more oxygen vacancies compared to the crystalline\nZnCr oxides. More active intermediate species would exist on the surface\nof the amorphous ZnCr oxides and within the pores of the SAPO-34 zeolite.\nSimultaneously, amorphous ZnCr oxides exhibited greater stability\ncompared to crystalline ZnCr oxides because structural reconstruction\nwould occur on crystalline ZnCr oxides, leading to the appearance\nand agglomeration of ZnO particles during harsh reaction conditions.\nConsequently, the bifunctional catalyst composed of amorphous ZnCr\noxides and SAPO-34 zeolites demonstrated superior catalytic activity\nand stability in syngas conversion. After reaction for 50 h, the bifunctional\ncatalyst maintained a CO conversion of 49.8% and a C<sub>2</sub><sup>=</sup>–C<sub>4</sub><sup>=</sup> selectivity of 80.2%, achieving\na space–time yield of 16.2 mmol·g<sup>–1</sup>·h<sup>–1</sup>. The findings suggest that controlling the structure\nof metal oxide is an efficient method for developing catalysts with\nhigh catalytic activity and stability in syngas conversion.